The invention described and claimed herein relates generally to hard disk drives used to store information in computers and particularly to an improved suspension assembly used in such hard disk drives.
Most personal computers today utilize direct access storage devices (DASD) or rigid disk drives for data storage and retrieval. Presently, a disk drive includes at least one disk that has a selectively magnetizable magnetic coating. In addition, a disk drive will include a read/write xe2x80x9cheadxe2x80x9d that is positioned a microscopic distance from the disk surface. During operation, the read/write head is said to xe2x80x9cflyxe2x80x9d over the disk as the disk is rotated at speeds currently ranging from 3600 revolutions per minute (rpm) to 15,000 rpm. Information is stored on or written to the disk by the selective magnetization of the disk""s magnetic coating and is retrieved or read from the disk by sensing the previous selective magnetizations. The read/write head is affixed to the disk drive by a suspension assembly and electrically connected to the disk drive electronics by an electrical interconnect. This structure (suspension, electrical interconnect, and read/write head) is commonly referred to in the industry as a Head Gimbal Assembly, or HGA. The read/write head, along with a slider, is disposed at the distal end of an electrical interconnect/suspension assembly.
More specifically, currently manufactured and sold read/write heads include an inductive write head and a magneto resistive (MR) read head or element or a xe2x80x9cgiantxe2x80x9d magneto resistive (GMR) element to read data that is stored on the magnetic media of the disk. The write head writes data to the disk by converting an electric signal into a magnetic field and then applying the magnetic field to the disk to magnetize it. The MR read head reads the data on the disk as it flies adjacent to it. To do this, a xe2x80x9csensexe2x80x9d current is sent through the read head. As the read head passes over the varying magnetized areas on the disk surface, a current will be induced in the read head according to well-known electromagnetic principles. This will result in a change in the sense current, which is accompanied by a change in the current voltage. The changes in the sense current or the sense current voltage in turn is converted into a binary data stream.
An exploded view of a typical electrical interconnect/suspension assembly is shown in FIG. 1, which illustrates several components including a suspension A and an interconnect B. It will be understood that the actual physical structures of these components may vary in configuration depending upon the particular disk drive manufacturer and that the assembly shown in FIG. 1 is meant to be illustrative of the prior art only. Typically, the suspension A will include a base plate C, a radius (spring region) D, a load beam E, and a flexure F. At least one tooling discontinuity G may be included. An interconnect B may include a base H, which may be a synthetic material such as a polyimide, that supports typically a plurality of electrical traces or leads I of the interconnect. The electrical interconnect B may also include a polymeric cover layer that encapsulates selected areas of the electrical traces or leads I.
Stated otherwise, suspension A is essentially a stainless steel support structure that is secured to an armature in the disk drive. The read/write head is attached to the tip of the suspension A with adhesive or some other means. The electrical interconnect B is terminated, that is, electrically connected, to bond pads on the read/write head and provides an electrically conductive path between the disk drive electronics at one end thereof and the read and write elements in the read/write head at the other end thereof. The electrical interconnect is usually comprised of individual electrical conductors supported by an insulating layer of polyimide and typically covered by a cover layer.
Successful operation of a hard disk drive is dependent upon many factors. Among them are the fly height and the geometric and physical characteristics of the HGA.
As mentioned previously, the slider is spaced a small distance, or fly height, apart from the spinning disk. The fly height must be controlled within a narrow range for the disk drive to operate successfully. As the fly height increases, the ability of the read/write head to read or write data to the disk diminishes; as the fly decreases, the slider can more easily hit the disk surface, commonly known as a xe2x80x9ccrashxe2x80x9d or as xe2x80x9ccrashing the drivexe2x80x9d and resulting in the permanent loss of stored data.
The fly height of the slider is partly determined by the characteristics of the head suspension assembly to which it is mounted. One of these characteristics is the vertical load, commonly referred to as the xe2x80x9cgram loadxe2x80x9d, imparted on the slider by the head suspension assembly. This vertical or gram load is directed normal to the surface of the disk in order to oppose the xe2x80x9cliftxe2x80x9d forces created by the air passing between the slider and the spinning disk. In other words, as the slider flies relative to the disk, the air flowing between the slider and the disk results in the creation of a lifting force that tends to push the slider away from the disk. The gram load is provided to counter those lift forces. This balancing of opposing forces is a delicate task since the fly height must be maintained within the desired range. As a result, head suspension assemblies are manufactured with a very precise gram load, typically with a tolerance of +0.2 grams.
Another factor determining slider fly height is the relative position of the head suspension assembly load center relative to the slider air bearing geometry. If this load center or xe2x80x9cload pointxe2x80x9d is mis-aligned relative to the air bearing surface of the slider, an undesired torque is placed on the slider, which can cause an undesired slider pitch and/or roll. If the slider pitches or rolls, the spacing of the read/write element from the disk surface will be affected because the pitching or rolling motion of the slider changes its orientation and thus the orientation of the read/write elements relative to the disk surface.
Yet another head suspension assembly characteristic that can have a significant effect upon the fly height of a slider is referred to as xe2x80x9cstatic attitude.xe2x80x9d Static attitude is the angular attitude of the gimbal to which the slider is mounted relative to disk surface. Typically, head suspension assemblies are manufactured with tolerances for static attitude approaching +30 arc-minutes and the gimbal stiffnesses are designed to be very low (or highly compliant) to allow the slider air bearing forces to correct for static attitude tolerances during operation. If the static attitude is outside the desired range, a torque can be imparted to the slider, which as previously noted, can create an undesired slider pitch and/or roll.
Successful reading or writing of data between the head and the spinning disk also requires that the head be precisely positioned relative to the location on the disk from which data is to be read or to which data is to be written. Presently, data is written to hard drives along circular xe2x80x9ctracksxe2x80x9d on the disk. If a mode of vibration in the load beam or gimbal creates or causes motion that in turn prompts the read/write element to move off the track to be read or written to, the hard drive""s ability to follow the data tracks, and thus read and write to the disk properly, will be compromised. Specifically, to resist off-track motion, the side to side or lateral gimbal stiffness is desirably kept high in the gimbal area. As such, great care is taken to design and manufacture head suspension assemblies so as to optimize the suspension""s vibrational, or resonant, performance. Traditionally, there exists a trade-off between the desire for high lateral stiffness and the desire for low pitch and roll stiffnesses.
During gimbal manufacture and use, gimbal vertical stiffnesses are desired to be high, thereby enabling the head suspension assembly to resist handling damage during the various manufacturing processes, to maintain slider position during shock event, and to maintain normal geometry under the designed pre-load. In the sense just used, xe2x80x9cverticalxe2x80x9d means perpendicular to the plane of the disk during operation. That is, it is desired that the gimbal resist motion toward and away from the disk surface to maintain the desired fly height for the reasons previously given. Many suspension products have a low vertical gimbal stiffness. Manufacturers of such products attempt to counter the negative effects of low vertical gimbal stiffness by restraining the vertical deflection of the HGA with the load point and also with motion limiting features. These xe2x80x9climitersxe2x80x9d are configured to be disposed a predetermined distance away from the gimbal during normal operation, but to engage and limit gimbal motion when the gimbal is subjected to handling damage, shock or other potential causes of poor performance or damage. Unfortunately, gimbal limiting devices are difficult to align and assemble precisely and they occupy critical space needed for other features, such as slider bond pads, manufacturing alignment holes, circuit trace routing, and load/unload features.
Currently, there are three basic configurations of electrical interconnect/suspension assemblies that are utilized in the disk drive industryxe2x80x94the Trace Suspension Assembly or TSA; the CIS; and the Flex Suspension Assembly or FSA. Each of the foregoing configurations is known as wireless suspension because individual, separately manufactured wires have been replaced by the leads of the TSA, CIS, or FSA.
In a TSA, the electrical interconnect is fabricated integrally with the flexure. The TSA flexure/interconnect is fabricated by selectively removing material from a laminate of stainless steel, polyimide, and copper. The TSA flexure/interconnect is then attached to a loadbeam, typically with one or more spot welds between the stainless steel layer of the TSA flexure/interconnect and the stainless steel of the loadbeam.
Another interconnect configuration, termed CIS, is very similar to TSA in that the CIS interconnect is also fabricated integrally with the flexure. The CIS interconnect/flexure, however, is fabricated with xe2x80x9cadditivexe2x80x9d processes, rather than xe2x80x9csubtractivexe2x80x9d processes like the TSA. The CIS interconnect/flexure is attached to a load beam in much the same manner as the TSA flexures and conventional flexures are, with one or more spot welds between the stainless steel of the flexure and that of the loadbeam.
The third and final interconnect/suspension configuration widely utilized today by disk drive assemblers, the FSA, includes what is essentially a flexible interconnect circuit. The flexible interconnect circuit consists of a base polymer, typically a polyimide, which supports copper traces, or leads. In this case, the interconnect circuit is fabricated independently from the flexure, and is later adhesively attached to a conventional head suspension assembly to form an FSA.
While the motivation for using a wireless suspension is to improve performance and reduce cost, current products have fallen short of one or both of these goals. A list of current technical and cost issues with the current products follows:
1) pitch and roll stiffnesses are not low enough for future requirements, which generally will require reduced fly heights;
2) gimbal vertical stiffnesses are too low and shock limiting features are required;
3) they are susceptible to handling damage;
4) under shock conditions the slider parallelism to the disk is not well maintained;
5) their pitch and roll static attitude changes significantly when subjected to temperature and humidity extremes;
6) they are difficult to manipulate during electrical termination, due to the spatial constraints caused by complex limiters, trace routings, and other constraints; and
7) they are expensive to manufacture due to the numerous extra steps during forming, welding, and manipulating.
As such, it is the object of the present invention to eliminate the performance and cost disadvantages of the current electrical interconnect/suspension assemblies.
It is an object of the present invention to provide a polymeric/copper gimbal suspension with significantly low gimbal pitch and roll stiffnesses while maintaining high lateral stiffnesses.
It is still another object of the present invention to provide a polymeric/copper gimbal suspension with significantly low gimbal stiffnesses and high vertical stiffness and the ability to limit slider motion during handling and shock events.
It is yet another object of the present invention to provide a polymeric/copper gimbal suspension which minimizes static attitude change due to temperature and humidity changes.
It is another object of the present invention to provide a polymeric/copper gimbal suspension which allows for a maximum amount of space for head electrical termination and manipulation.
It is another object of the present invention to eliminate the welding of a stainless steel gimbal to a load beam during suspension manufacturing.
It is yet another object of the present invention to eliminate stainless steel gimbal etching, forming, and manipulation during suspension manufacturing.
It is still a further object of the present invention to provide a method for assembling the read/write head slider to the circuit, making an electrical termination, and then attaching the flexible circuit/head/slider assembly to the suspension, while simplifying each and every manufacturing step and improving static attitude and load point control.
The present invention is directed to an integral electrical interconnect/suspension assembly that positions a read/write magnetic transducer head adjacent the rotating surface of a disk in a disk drive from an actuator arm of the disk drive, and the method of constructing the head suspension assembly. The head suspension is disclosed in various embodiments, all including specific polymeric/copper ring gimbals to both improve the performance characteristics and lower the cost to manufacture and use these products.
More specifically, the present invention as described and illustrated herein includes a polymeric/copper ring gimbal adhesively attached to a load beam. A gimbal according to the present invention further includes at least one deformation inhibiter for inhibiting and/or preventing the deformation of the gimbal due to humidity. In one embodiment of the present invention, the inhibiter may include a forwardly or distally extending appendage. Such a deformation inhibiting appendage may be an extension of the conductive traces forming the electrical pathway on the gimbal. Preferably, such inhibiters are resistant to the absorption of water, unlike the polymeric substrate of the gimbal.
The foregoing objects of the invention will become apparent to those skilled in the art when the following detailed description of the invention is read in conjunction with the accompanying drawings.